Obviously true, and requiring no proof, argument or explanation.

Of a person, having achieved success by one's own efforts, with little to no support from family members and others. / Of a thing, made by oneself instead of bought or taken over.

The means of defending oneself from physical attack.

(linear algebra) Of a vector space, isomorphic to its dual space. / (mathematics, in projective geometry) Of a proposition that is equivalent to its dual.

Able to provide for one's own needs without help from others; self-sufficient. / (of a nuclear chain reaction) Able to sustain itself without the need for additional fuel.

Having, or behaving as if having, too high of an opinion of one's own importance.

Able to generate a copy of itself.

A reminder to oneself to do something important.

determined to advance one's own personality or views

The quality of being self-evident.